Same error here.
My Fix: I remembered that I left my plug ins on during the upgrade. So, I pointed to the plugins page manually. It came up and I disabled the plugins and it worked after that.
Hmmm. That kind of stinks. For instance, my last post was initially a test post for an embeded video pluging I was testing. When I was done, I used that same post to write a serious post. The slug, unless the developers changed how it works, will retain the slug value of “test-video”.
:/
I used default permalinks in WP < 2.5. However, sometimes I would still edit slugs just in case I switched to another mode. Is there a way to edit the slug in default mode?